In the field of industrial automation engineering, motor starters are used for the operational switching of motor loads. Here, a switch unit of the motor starter controls, i.e. connects or disconnects, the supply voltage of a consumer, in particular an electric motor. Suitable embodiments of motor starters are also able to cover safety-relevant applications according to EN 13849 or IEC 61508.
For safety-oriented applications, the motor starter must have a secure design. For a secure design of a motor starter, it is necessary to provide redundancy in the motor starter. For example, two normal switching elements of the switch unit are connected in series for the same function. If the two switching elements also have a different design, this provides a diverse system. To ensure that a switch unit has a secure design, it must comprise at least two switching elements for switching a line.
F-starters of the ET200S series made by the company Siemens are examples of redundant diverse motor starters. In these starters, redundancy and diversity is achieved by the serial arrangement of a circuit breaker with an overvoltage release and contactor.
Decentralized sensors (for example emergency stop buttons) can be used to control the motor starter by means of a sensor signal so that the motor starter can react accordingly.
In the case of a secure motor starter, a sensor signal of this kind is evaluated by way of a security evaluation unit of the motor starter. To this end, this security evaluation unit is connected to the sensor on the input side and to a secure switch unit of the motor control unit on the output side. The task of the security evaluation unit is to process the sensor signals of the sensor securely and to monitor them securely. Another task of the security evaluation unit is to monitor the correct function of the secure switch unit of the motor starter securely. For example, in the event of welding of one of the two switching elements of the secure switch unit, the reconnection of the two switching elements can be prevented by the security evaluation unit.
The connection of the security evaluation unit to the secure switch unit is currently achieved by way of the customer wiring the two units together. However, this means more work for the customer and a risk of error. It may also entail additional work to rectify errors in the case of faulty cabling and/or additional work for protected cable laying.